About stag beetles

Status

Nationally scarce

Population

unknown

Latin name

Lucanus cervus

Stag beetles are one of the most spectacular looking insects in Britain, named because the male’s large jaws look just like the antlers of a stag. As well as being one of the largest, they are sadly one of our rarer beetles.
They spend most of their life underground as larvae, only emerging for a few weeks to find a mate and reproduce. Stag beetles and their larvae are quite harmless and a joy to watch.

Identification

Stag beetles are harmless and do not damage living wood or timber. The larvae only feed on decaying wood so please do not kill them.

Stag beetles are also known commonly known as horse pinchers, thunder beetles and oak ox. Their head and thorax (middle section) are shiny black and its wing cases are chestnut brown.

Male beetles appear to have huge antlers. They are actually over-sized mandibles, used in courtship displays and to wrestle other male beetles. They are not harmful to humans. Adult males can vary in size from 35mm – 75mm long and tend to be seen flying at dusk in the summer looking for a mate.

Female beetles are smaller at between 30-50mm long, with smaller mandibles. They are often seen on the ground looking for somewhere to lay their eggs.

A fully-grown stag beetle larva (grub) can be up to 110mm long. They are fairly smooth skinned, have orange head and legs and brown jaws. They are nearly always found below ground and can be as deep as half a meter down.

Male and female stag beetles by Ross Bower

The beetle that is most often mistaken for a female stag beetle is the lesser stag beetle. However, the lesser stag is uniformly black all over with matt wing cases, while the female stag beetle has shiny brown or maroon wing cases. Lesser stag beetles tend to have a much squarer overall look.

Habitat and distribution

Stag beetles live in woodland edges, hedgerows, traditional orchards, parks and gardens throughout Western Europe including Britain- but not Ireland. Stag beetles are relatively widespread in southern England. They are also found in the Severn valley and coastal areas of the southwest. Elsewhere in Britain they are extremely rare or even extinct.

Female stag beetles prefer light soils which are easier to dig down into and lay their eggs. Newly emerging adults also have to dig their way up through the soil to reach the surface. Areas like the North and South Downs, which are chalky, have very few stag beetles. They also prefer areas which have the highest average air temperatures and lowest rainfall throughout the year.

We are particularly keen for people to record stag beetles in the counties on the border of their known range including Cambridgeshire, Devon, Gloucestershire, Lincolnshire, Norfolk, Warwickshire, Worcestershire and Yorkshire. Please keep a special eye open if you are visiting the following places: Richmond Park, Wimbledon Common, the New Forest and Epping Forest.

Diet

Larvae feed on decaying wood under the ground. Adults can’t feed on solid food – they rely on the fat reserves built up whilst developing as a larva. They are able to drink from sap runs and fallen soft fruit.

Habits

Stag beetle larvae by Peter Cox

Stag beetles spend the majority of their very long life cycle underground as a larva. This can be anywhere from three to seven years depending on the weather. Periods of very cold weather can extend the process. Once fully grown, the larvae leave the rotting wood they have been feeding on to build a large ovoid cocoon in the soil where they pupate and finally metamorphose into an adult. Adults spend the winter underground in the soil and usually emerge from mid-May onwards. By the end of August, most of them will have died. They do not survive the winter.

During their short adult lives the male stag beetles will spend their days sunning themselves in an attempt to gather strength for the evening’s activities of flying in search of a mate. This is when you are most likely to spot them.

Breeding

Although they can fly, female beetles are most often seen walking around on the ground. Once they have mated, the females return to the spot where they emerged, if there is enough rotting wood to feed their young, and dig down into the soil to lay their small, round eggs in rotting wood such as log piles, tree stumps and old fence posts. Males tend to be seen flying around at dusk searching for a mate.

Predators

Predators such as cats, foxes, crows, kestrels and others tend to strike at the most vulnerable stage in the beetle’s life cycle, when adults are seeking to mate and lay eggs. Though this is largely natural predation, it has been suggested that the rise in the numbers of magpies and carrion crows in the last decade may be having a significant impact on stag beetle populations.

Threats

A vertical log pile is ideal for stag beetles

The most obvious problem for stag beetles is a significant loss of habitat. Many woodlands were sold for development during the inter-War years. The introduction of the Green Belt in 1947 did restrict suburban expansion but since then many of London’s surviving open spaces have sadly been developed, including many woodlands. Development will continue to reduce stag beetle habitats, but increased awareness of their existence can help defend the beetles against development.

In addition the ‘tidying up’ of woodlands, parks and gardens has led to the removal of dead or decaying wood habitats which is the stag beetle larvae’s food source. Tree surgery operations such as stump-grinding of felled trees removes a vital habitat for the beetle. Although ‘tidying up’ still continues in gardens, woodlands and park managers are now much more aware of the need to retain dead and decaying wood as part of the woodland ecosystem. The Royal Parks’ management plans for Richmond Park, among others, include the retention of suitable dead wood to help encourage stag beetles.

Humans are, unfortunately, a direct threat to the stag beetle. Adult beetles are attracted to the warm surfaces of tarmac and pavements, making them particularly vulnerable to being crushed by traffic or feet. Stag beetles have a fearsome appearance and sometimes people kill them because they look ‘dangerous’.

Changes in weather patterns are also likely to have an impact on stag beetles. Exceptionally dry or wet weather is likely to substantially affect the larvae. Wet and windy weather can inhibit adult beetles’ flying ability.

Status and conservation

The stag beetle is legally protected from sale in the UK. It is also classed as a ‘protected species’, listed on Schedule 5 of the Wildlife and Countryside Act 1981. If stag beetles and/or stag beetle larvae are known or thought to be present at a site where an application for planning has been submitted, and are likely to be disturbed or destroyed whilst work is carried out at the site, it is recommended that someone with an understanding of the insects’ requirements be present to see that any larvae and/or adults are carefully translocated to a suitable natural or purpose-built habitat close by.

It is Red listed in many European countries and has undergone a decline across Europe. Stag beetles are now extinct in Denmark and Latvia.

How you can help!

If you find an adult stag beetle, please leave it where it is, unless it is in danger of being run over or
trodden on. If you have to move a beetle for its own safety, then please move it as short a distance
as possible. You can give it some soft fruit or sugar water. If you dig up a stag beetle larva, please put it back exactly where you found it. The next best thing is to re-bury the larva in a safe shady place in your garden with as much of the original rotting wood as possible.

Useful stag beetle links

Stagbeetle.infoWebsite dedicated to stag beetles from our partners at Royal Holloway, University of London

Stag beetle video
Short film of stag beetles in action from the Natural History Museum.

Database of insects and their food plants
This database is primarily a collation of published interactions between Great Britain ‘s invertebrate herbivores (insects and mites) and their host plants. DBIF aims to help researchers access the accumulated knowledge of British plant-herbivore interactions, which is otherwise scattered throughout a vast published literature.